Excess light or pH problem?

Good afternoon, in your opinion is this excess light or just a pH problem?
My lights are 4 x Cxb3590 at 55w each. I think the problem comes from the side of my ph meter since the lights are more than 50cm high
EC : 0.9 / 1.0
Supplement Cal Mag

I always calibrate my meter and it shows me the correct readings as if it were calibrated. It is an HM PH-200.

Doesn't look like a PH issue, back the lights off and see if they return to normal growth.

Looks more nutrient related than light to me. Could be that your ph is locking out some elements. Looks like maybe zinc or iron deficiency. A ph over 6 in hydro can make iron harder for the plants to get, depending on chelation, but the leaf veins are supposed to be green in an iron deficient plant and those are pretty pale.
Not nitrogen as the older leaves are green, it’s mostly the new upper growth that’s lime green.
I’m thinking zinc deficiency unless there’s some bad ph issues or some other info.
Decent chart in this thread.

My meter is the one on the right, it turns out the problem is coming from the meter.

pH would be my first thought.

Always good to have 2 meters so good idea that you picked up that other one.